linux-kernel - Re: [RFC PATCH 3/5] drm/i915: register LVDS connector even if we can't get a panel mode

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Message-ID: <CADnq5_ORRL++gB_Xh9a3vTMf8PeQ92npAcA0P5QdxAhpVM8Wig@mail.gmail.com>
Date:	Sun, 5 Aug 2012 19:20:31 -0400
From:	Alex Deucher <alexdeucher@...il.com>
To:	Dave Airlie <airlied@...il.com>
Cc:	Matthew Garrett <mjg59@...f.ucam.org>,
	dri-devel@...ts.freedesktop.org, David Airlie <airlied@...ux.ie>,
	linux-kernel@...r.kernel.org, Andreas Heider <andreas@...tr.de>
Subject: Re: [RFC PATCH 3/5] drm/i915: register LVDS connector even if we
 can't get a panel mode

On Sun, Aug 5, 2012 at 5:44 PM, Dave Airlie <airlied@...il.com> wrote:
> On Mon, Aug 6, 2012 at 7:40 AM, Daniel Vetter <daniel@...ll.ch> wrote:
>> On Sun, Aug 05, 2012 at 10:18:38PM +0100, Matthew Garrett wrote:
>>> On Sun, Aug 05, 2012 at 11:14:12PM +0200, Daniel Vetter wrote:
>>>
>>> > I like this approach more - the only other solution I see is to ask the
>>> > currently active driver (i.e. radeon) at bootime for the right mode. Which
>>> > sounds much more hellish and fragile ...
>>>
>>> The "correct" approach is clearly to just have the drm core change the
>>> i2c mux before requesting edid, but that's made difficult because of the
>>> absence of ordering guarantees in initialisation. I don't like quirking
>>> this, since we're then back to the situation of potentially having to
>>> add every new piece of related hardware to the quirk list.
>>
>> The "correct" approach of switching the mux before we fetch the edid is
>> actualy the one I fear will result in fragile code: Only run on few
>> machines, and as you say with tons of funky interactions with the init
>> sequence ordering. And I guess people will bitch&moan about the flickering
>> this will cause ;-)
>>
>> As long as it's only apple shipping multi-gpu machines with
>> broken/non-existing vbt, I'll happily stomach the quirk list entries.
>> They're bad, but imo the lesser evil.
>
> Well in theory you can switch the ddc lines without switching the other lines,
> so we could do a mutex protected mux switch around edid retrival,
>

Depends on the system.  On non-Macs, some systems have a single mux,
others have a separate mux for i2c and display as specified in the
ATPX ACPI methods.  Not sure how the Macs do it.  I've started
cleaning up the PX radeon code along with a bunch of other radeon
ralated ACPI fixes:
http://cgit.freedesktop.org/~agd5f/linux/log/?h=acpi_patches

Alex
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